Pancake Day is another name for Shrove Tuesday which is the day before Lent.  Lent is a Christian event that was established in the 4th century as 40 days and is usually a period of fasting.  Today people might say that they give up chocolate for Lent.  People generally eat a lot and have fun the day before Lent begins. Shrove Tuesday is often referred to as Pancake Day because fats, which were generally not used during Lent, had to be used up. People would take all the eggs and dairy products that they had left in their kitchens and use them to make delicious pancakes.
In the U K and several other countries around the world, Pancake Day is celebrated with fun, games, and of course a lot of eating. However, the most well known activity on this day is the Pancake Day race at Olney in Buckinghamshire, England which has been held since 1445. It all began when a woman was cooking pancakes on Shrove Tuesday to use up all of her eggs and fats before Lent.  While she was still cooking she heard the chiming of the bells summoning her to church.  Not wanting to be late, the woman ran to church with her apron on and the frying pan still in her hand.  Little did she know that this would start a tradition that would be around for over 500 years!
Originally only women were allowed to participate in this race. They must run a designated path with a frying pan and end up at the church. They must have a hot pancake in the frying pan which they must flip at least three times before they complete the race. The first woman to complete the race and arrive at church with the pancake is declared the winner. She then serves the pancake to the bellringer and is rewarded with a kiss from the bellringer called the “Kiss of peace”. This race still occurs in England and in several other cities.

There are now Pancake Races in most towns and now they are used to fund raise for charities.

Here you can see a video clip from Olney - the town where the first pancake race was held.